My current template took me a loooong time to do!
First, I edited or replaced every single lot in every single world. Some were minor edits, some were overhauls. Some lots I built myself, some I downloaded. Added any lot traits I wanted. I included a graveyard, some 'work' buildings, all the usual lots like library, gym, cafe, bars etc, a small starter vet practice ready for purchase, a small starter empty retail lot and a bakery and also some community spaces from Eco.
Then I set about the households. For the premades, I edited their hot and cold outfits since those were randomly assigned. Then I placed in all my favourite remade families from TS2 and TS3. Then I added all the sims I have ever created and played (I keep some old saves, so imported them from those). So I now have almost every residential lot occupied.
I'm currently playing that template, slowly getting through the households :)